Method and mix composition for producing oxidation resistant carbon articles



United States Patent METHOD AND MIX COMPOSITION FOR PRO- DUCINGOXIDATION RESISTANT CARBON ARTICLES Charles S. Lowe, Niagara Falls,N.Y., and John D. Nickerson, Lakeland, Fla., assignors to Union CarbideCorporation, a corporation of New York No Drawing. Filed Oct. 24, 1958,Ser. No. 769,296

5 Claims. (Cl. 106-56) This invention refers to oxidation resistantcarbon articles and more particularly refers to a method and mixcomposition for producing the same.

Refractory articles composed of carbon, such as for example, furnacelining brick, are made conventionally by mixing comminuted particles ofcarbon and a carbonizable binder therefor, molding the mixture to adesired shape and then baking the shape to a carbonizing temperature.Similarly, furnace electrodes are made in much the same manner. Whenarticles of this nature are employed in furnaces in the presence of anoxidizing atmosphere, a continuous oxidation of the carbon takes place.The brick is usually oxidized from the interior of the furnace to thefurnace wall and the electrodes are generally oxidized from the interiorsurface to the center thereof.

In the prior art various expedients have been employed for applyingprotective films to carbon articles to protect them against oxidation.Among these are the employment of phosphoric acid, boro-phosphoric acidand inorganic phosphate salts. The listed materials are generallyintroduced into the pores of a formed carbon body by impregnating itwith the acid itself, or with a solution of a phosphate salt dissolvedin phosphoric acid. For impregnating a formed body, an aqueous solutionof certain phosphates may be used or impregnation may be attained byalternately impregnating with a solution of a metallic halide andphosphoric acid. When impregnating with a solution such as one ofphosphoric acid, the protection thus afforded to the treated carbon islimited by the amount of acid that can be absorbed, and by itsvolatilizing temperature. Phosphates may also be provided in a carbonbody by the direct addition of phosphate salts to the mix from which itis formed.

Phosphorus-containing organic compounds have been used in the past byvarious workers in this general field of carbon article technology toprovide a plasticizing elfect on the carbon material from which they areformed. This enables forming of such material at substantially reducedpressures and temperatures than would be possible without the use ofsuch compounds. In most of the instances of such use, the carbonmaterial which has been plasticized by the phosphorus-containing organiccompound has been in the 'raw or uncalcined state. Sometimes noadditional pitch binder is necessary or used since the volatilecomponents of the uncalcined carbon form the necessary coking binder forthe finished article. One of the great disadvantages of using uncalcinedcarbon lies in the fact that there is a great'amount of shrinkage of thearticle upon baking; Tests have shown that by calcining carbon materialto be formed into articles, the shrinkage in the article which occursduring baking has been reduced up to as much as times, thus allowing theforming and baking of large dimension articles without the danger ofexcessive shrinkage destroying the article made. Usually calcining isdone at temperatures around 1000 C. or higher depending upon the carbonsource and the baking temperature of the article. It is highlyadvantageous, especially when large dimension articles are desired, tocalcine the carbon material before forming and baking in order to reducethe volatiles content of the carbon and therefor reduce shrinkage. I

It is therefore the object of this invention to provide a novel methodand mix composition for producing a carbon article which issubstantially resistant to oxidizing atmospheres which are present inmost furnaces and which will have reduced volume shrinkage upon baking.

Fulfilling this object, the invention comprises a method for producingan oxidation resistant carbon article from a mix composition composedsubstantially of calcined carbon and containing as an essentialingredient therein at least one phosphorus-containing,oxidation-inhibiting, pitch-miscible, organic compound in an efiectiveamount up to 10% in the aggregate by weight of the entire mix. It is thephosphorus-containing compound which imparts the oxidation resistance tothe article in question. More specifically, aliphatic, aromatic andalkyl-aryl phosphates have been found to be the most elfective materialsto be used as mix additives in providing carbon articles with longerdurability and greater ability to Withstand the action of oxidizingconditions.

Among the compounds which have given practical results in the practiceof this invention are tri-cresyl phosphate, tri-ethyl phosphate, methylacid phosphate, bis (2- ethylhexyl) Z-ethylhexyl phosphonate, cresyldiphenyl phosphate, tri-iso-octyl phosphite, di-Z-ethylhexyl phosphite,tri-butyl phosphate, tri-phenyl phosphate and octyl di-phenyl phosphate.

It has been found that calcined carbon, that is carbon which hassubstantially no volatile content, works best in the practice of this.invention if it has an ash content of at least 0.25%. It has furtherbeen found thatthe final baking temperature of the formed carbonarticles need not exceed 1200 C. in order to impart the protectiondesired in the baked article. More particularly, calcined coal basearticles made with organic phosphate additives have been baked tobetween 800 and 1000 C. and calcined petroleum coke base articles havebeen baked to approximately 750 C. in order to impart the desiredprotection.

Various articles have been made according to this invention and testedfor their resistance to oxidation by the following procedure: Theweighed samples were put in aluminum dishes, which were placed on a inchthick copper plate placed in an oven at 450 C. to 600 C. Before eachweighing, the samples were rolled to remove material which might haveloosened because of the oxidation of the carbon bond. Oxidation testswere also carried out above 600 C. by placing the samples directly uponthe copper plate.

The following may be cited as specific examples of mix formulationswhich have been experimentally formed to provide carbon articles whichare resistant to oxidation.

A dry mix of 165 pounds of petroleum coke particles and pounds of 55%petroleum coke flour each calcined to 1350 C. was made. To this basicdry mix, 78.6 pounds of coal tar pitch and .4.8 pounds of lubricatingoil were added and the resultant mass extruded at conventional pressureand temperature, and baked to 750 C. to form 4 inch diameter by 15 incharticles.

The same proportions of basic dry mix, petroleum coke flour andparticles calcined at the same temperature were blended with 70 poundsof coal tar pitch, 4gpounds of lubricating oil and 10.5 pounds oftri-cresyl phosphate and the resultant mix molded and baked as above.The results of tests conducted on these articles appear-in Table Ibelow. The proportions of additives are. shown in parentheses based uponweight percent of the entire mix.

Patented June 20, 1961' A coal base article having no oxidationinhibiting additive was made by dry blending 200 pounds of coal and 133pounds of 45% foundry coke flour each calcined to 2000 C. and mixingthis'blend with 95 pounds of coal tar pitch and pounds of lubricatingoil. This wet mix Was molded at conventional pressure and temperature,and baked to 950 C. to form 4 inch diameter by inch articles.

A dry mix of 215 pounds of coal and 143 pounds of foundry coke floureach calcined at 2000 C. was blended with 90 pounds of coal tar pitchand 4.5 pounds of tri-cresyl phosphate, molded and baked as above notedto give 4 inch diameter by 15 inch articles containing 1% tri-cresylphosphate by weight of the entire mix.

A dry mix of 215 pounds of coal and 143 pounds'of 45% foundry cokefiour'each calcined to 2000 C. was blended with 81 pounds of coal tarpitch and 15 pounds of tri-cresyl phosphate to give a mix containing3.4% tri-cresyl phosphate. The mix was molded and baked as abovedescribed into 4 inch diameter by 15 inch articles. All the articlesmade in accord with the above three examples were tested as to theirability to Withstand oxidation at elevated temperatures and the resultsof these tests appear in Table II below.

Table II Percent Weight Percent Weight Percent Vol. Loss at 485 0. Lossat 700 C. Shrinkage of Coal Stock In Air In Air formed articles oninitial baking to 5.5 Hrs. 17 Hrs. 4.0 Hrs. 8.0 Hrs. 950 G.

Control -1 2. 87 72. 9 20. 2 32. 3 0. 34 TOP (3 4) 1. 40 13. 5 17. 7 26.9 1. 47 TOP (1 0) 2.35 16.3 18.8 30.7 1. 51

Additives other than tri-cresyl phosphate have been added to calcinedcarbon base articles and tested for resistance'to oxidation. The resultsof these tests appear in Table III below.

As shown by the above tables, the percent weight loss rate in air ofcarbon articles has been substantially reduced by the inclusion of minoramounts of organic phosphates as described above. It is also to be notedthat there has been a slight increase in volume shrinkage by theaddition of minor amounts of organic phosphates. Also observed, but notindicated in the tables was an increase in the apparent" density of coalbase articles with the organic phosphate additive.

Articles as large as 12 inches in diameter have been made using thepractice of this invention and have with stood furnace operation underoxidizing conditions significantly better than similar articles with nooxidation inhibitor added thereto have in the past.

It may be convenient, without departing from the spirit and scope ofthis invention, to add a lubricating oil such as summer oil, prior tomolding in order to increase the plasticity of the mix. It is notessential to the practice of this invention and may or may not beincluded.

This application is a continuation-in-part of Serial No. 574,085, filedMarch 27, 1956, now abandoned.

What is claimed is:

1. A mix adapted to be baked into an oxidation resistant carbon articlewhich comprises calcined comminuted carbon, a pitch binder therefore inan amount of up to 20% by weight of said mix and at least one compoundselected from the group consisting of tri-cresyl phosphate, tri-ethylphosphate, methyl acid phosphate, bis (2, ethylhexyl)2-ethylhexylphosphonate, cresyl dipenyl phosphate, tri-iso-octyl phosphite,di-Z-ethylhexyl phosphite, tri-butyl phosphate, tri-phenyl phosphate andoctyl di-phenyl phosphate, said compound being present in said mix in aneffective amount up to 10% in the aggregate by weight thereof, saidcompound being an essential constituent therein and imparting saidoxidation resistance to said article.

2. A mix adapted to be baked into an oxidation resistant carbon articlewhich comprises calcined comminuted carbon having at least 0.25% ashcontent, a pitch binder therefor in an amount of up to 20% by weight ofsaid mix and at least one compound selected from the group consisting oftri-cresyl phosphate, tri-ethyl phosphate, methyl acid phosphate, bis(Z-ethylhexyl) 2- ethylhexyl phosphonate, cresyl diphenyl phosphate,triiso-octyl phosphite, di-2-ethylhexyl phosphite, tri-butyl phosphate,tri-phenyl phosphate and octyl di-phenyl phosphate, said compound beingpresent in said mix in an effective amount up to 10% in the aggregate byweight thereof, said compound being an essential constituent therein andimparting said oxidation resistance to said article.

3. The method of making an oxidation resistant carbon article whichcomprises mixing calcined comminuted carbon, a pitch binder therefor inan amount of up to 20% by weight of said mix, and an effective amount upto 10% by weight of said mix of at least one compound selected from thegroup consisting of tri-cresyl phosphate, tri-ethyl phosphate, methylacid phosphate, bis (Z-ethylhexyl) Z-ethylhexyl phosphonate, cresyldiphenyl phosphate, tri-iso-octyl phosphite, di-Z-ethylhexyl phosphite,tri-butyl phosphate, tri-phenyl phosphate and octyl diphenyl phosphate,forming said mix into a desired shape and baking said molded shape to acarbonizing temperaturc.

4. The method of making an oxidation resistant carbon article whichcomprises mixing calcined comminuted carbon having an ash content of atleast 0.25%, a pitch binder therefor in an amount of up to 20% by weightof said mix, and an effective amount up to 10% by weight of said mix ofat least one compound selected from the group consisting of tri-cresylphosphate, tri-ethyl phosphate, methyl acid phosphate, bis(Z-cthylhexyl) Z-ethylhexyl phosphonate, cresyl diphenyl phosphate,tri-isooctyl phosphite, di-2-ethylhexyl phosphite, tri-butyl phosphate,tri-phenyl phosphate and octyl di-phenyl phosphate, forming said mixinto a desired shape and baking said molded shape to a carbonizingtemperature.

5. The method of making an oxidation resistant carbon article whichcomprises mixing calcined comminuted carbon having an ash content of atleast 0.25%, a pitch binder therefor in an amount of up to 20% by weightof said mix, and an eifective amount up to 10% by weight of said mix ofat least one compound selected from the group consisting of tri-cresylphosphate, triethyl phosphate, methyl acid phosphate, bis (Z-ethylhexyl)Z-ethylhexyl phosphonate, cresyl diphenyl phosphate, tri-iso-oetylphosphite, di-Z-ethylhexyl phosphite, tri-butyl phosphate, tri-phenylphosphate and octyl diphenyl phosphate, forming said mix into a desiredshape and baking said molded shape to a carbonizing temperature up to1200' C.

References Cited in the file of this patent UNITED STATES PATENTSBangham et a1. July 16, 19,46 'Sejersted et a1 Sept. 29, 1953 Woodbum eta1. Aug. 3, 1954 FOREIGN PATENTS Great Britain Jan. 10, 1951 UNITEDSTATES PATENT. OFFICE CERTIFICATE OF CORRECTION Patent No. 2,989,408June 20., c1961 Charles S. Lowe et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 25, for "interior" read exterior Signed and sealed this6th day of March 1962.

( SEA L) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. A MIX ADAPTED TO BE BAKED INTO AN OXIDATION RESISTANT CARBON ARTICLEWHICH COMPRISES CALCINED COMMINUTED CARBON, A PITCH BINDER THEREFORE INAN AMOUNT OF UP TO 20% BY WEIGHT OF SAID MIX AND AT LEAST ONE COMPOUNDSELECTED FROM THE GROUP CONSISTING OF TRI-CRESYL PHOSPHATE, TRI-ETHYLPHOSPHATE, METHYL ACID PHOSPHATE, BIS (2, ETHYLHEXYL) --ETHYLHEXYLPHOSPHONATE, CRESYL DIPENYL PHOSPHATE, TRI-ISO-OCTYL PHOSPHITE,DI-2-ETHYLHEXYL PHOSPHITE, TRI-BUTYL PHOSPHATE, TRI-PHENYL PHOSPHATE ANDOCTYL DI-PHENYL PHOSPHATE, SAID COMPOUND BEING PRESENT IN SAID MIX IN ANEFFECTIVE AMOUNT UP TO 10% IN THE AGGREGATE BY WEIGHT THEREOF, SAIDCOMPOUND BEING AN ESSENTIAL CONSTITUENT THEREIN AND IMPARTING SAIDOXIDATION RESISTANCE TO SAID ARTICLE.